I have been in the National Guard for six years now, ever since my senior year of high school. It is undoubtably the defining decision of my life. Basic training and AIT turned me into a man, and I was able to go to college for free. The Florida Guard pays 100% tuition assistance at all state-funded colleges and universites (no private schools), and the GI Bill check is always a nice little surprise in the mail. A few things I think you should know, however, based on my personal experiences.
First of all, don't let the recruiter tell you that as a college student you will be exempt from wartime callups or national emergency activations. I was told that college students don't have to go anywhere during school, and I have never found this to be true. I have had to drop classes during three separate semesters because of deployments, hurricanes, etc. Expect it, if you join. The Guard will always come first, especially since they are the ones paying for your school.
Another thing, the Guard is not the regular army, much as it sometimes tries to be. I consider myself a good soldier (always pass PT text, expert weapons, never awol, etc.) and am very often dissapointed with the low standards and "old-boy" system that the guard is subject to. If you are a good soldier, plan on carrying the load of the bad soldiers, and watching them get away with things you wouldn't dream of doing, all the time.
If I could do things differently, I would have joined the Infantry unit down south, rather than the Air Defence unit I am in, so that I could have attended Air Assault school and all the other high speed stuff they do.
Lastly, if you are thinking about joining a unit, go drill with them one weekend before you sign up, just to make sure. Many times I have seen high school kids in civvies come out to the field with us and play around with the systems before they join up. Every unit should be willing to let you do this as an enticement to join up, and it is a great way to help yourself decide what you really want.